Medical catheters having a balloon mounted thereon are useful in a variety of medical procedures. Balloon catheters may be used to widen a vessel into which the catheter is inserted by dilating the blocked vessel, such as in an angioplasty procedure. Balloon catheters may also be used to expand and/or seat a medical device such as a stent or graft at a desired position within a body lumen. In all of these applications, fluid under pressure is supplied to the balloon through an inflation lumen in the catheter, thereby expanding the balloon.
It is essential in the manufacture of balloon catheters to properly seal the balloon to the catheter. The seal must be able to withstand the high pressures to which it is subjected on inflation of the balloon. A poor seal may result in leakage of inflation fluid and inability to achieve the desired pressure or even rapid loss of pressure and deflation of the balloon.
A number of methods for sealing a balloon to a catheter are known in the art. One such method involves the use of a suitable adhesive to bond the balloon to the catheter tube as disclosed, iter alia, in U.S. Pat. No. 4,913,701 to Tower and U.S. Pat. No. 4,943,278 to Euteneuer et al. The use of adhesives, however, adds to the thickness of the catheter and increase its rigidity at the region of the bonds. Moreover, adhesive bonds are known to be generally inferior to fusion bonds.
Another such method, where heat fusible materials are employed, involves the application of heat to fuse the balloon to the catheter tube. To that end, resistance heating of copper jaws has been employed to fuse a balloon to a catheter tube. Resistance heating, however, is known to result in the formation of small, random channels at the balloon-catheter interface, giving rise to undesirable variations in the strength of different bonds. The heat also causes undesirable crystallization and stiffening of the balloon and catheter material, not only at the bond site, but also in both directions axially of the bond, due to heat conduction through the balloon and the catheter, and heat radiation from the jaws.
A non-contact method for heat sealing a balloon onto a catheter is disclosed in U.S. Pat. No. 4,251,305 to Becker et al. A length of thin tubing is slid over an elongated shaft of the catheter and shrink tubing installed over the thin walled tubing at its ends overlapping the catheter shaft. The shrink tubing is partially shrunk. Lamps emitting energy along the visible and infrared spectra are used to provide radiant energy to form gradually tapering thermoplastic joints that bond the tubing and shaft. This method, nevertheless, suffers from the problem of undesired heat transfer along the catheter and balloon.
Yet another fusion-based method disclosed in U.S. Pat. No. 5,501,759 to Forman involves the use of a beam of laser radiation at a wavelength selected to at least approximately match a wavelength of maximum spectral absorption of the polymeric materials forming the balloon member and body. The polymeric materials are melted by the radiation and then allowed to cool and solidify to form a fusion bond between the catheter tube and the balloon. In order to bond the balloon about its entire circumference to the catheter tube, the catheter tube may be rotated relative to the laser beam or the laser beam may be rotated relative to the catheter tube.
In the former case, rotation speeds of 400 rpm or higher are necessary to ensure even heating of the catheter tube and balloon material. Care must be taken, however, to avoid damaging the catheter during rotation. Where a stent is mounted on the balloon, rotation of the catheter is even more difficult because of issues of stent securement. Moreover, the process can be slow because of the time required for the motor to attain the desired speed.
In the latter case, rotation of the beam relative to the catheter may be effected via the use of mirrors and focusing lenses. Alignment is difficult to achieve and maintain in such a system because of vibration from moving parts. The process is slow because of the time involved in loading and unloading the catheter and waiting for the rotational beam to reach the desired speed. Moreover, such an arrangement can be expensive to build.
Another fusion-based method disclosed in Forman involves the simultaneous use of multiple beams of energy to supply energy at discrete points about the circumference of the balloon and thereby heat the balloon. A single beam is split into multiple discrete beams and the multiple discrete beams directed about the circumference of the balloon via fiber optics.
For the purpose of this disclosure, all US patents and patent applications referenced herein are incorporated herein by reference in their entirety.
The invention in various of its embodiment is summarized below. Additional details of the invention and/or additional embodiments of the invention may be found in the Detailed Description of the Invention below.